Computers typically use modems to communicate digital information over voice-grade telephone lines. Such modems translate digitally expressed information from the computer into analog tone signals suitable for transmission over the voice-grade telephone facility, and convert such tones back into digital form when received from the telephone line.
High speed modems may advantageously employ digital signal processing techniques for translating outgoing digital data into a sequence of digital values each representing a desired analog output signal sample amplitude. These digital sample values may then be converted into analog form by a digital-to-analog converter for transmission over the telephone facility., Correspondingly, at the receiving station, the incoming analog signal may be converted into a train of digital sample amplitude values which are then processed to reconstruct the original digital data.
The processing of the digital sample values is complex and has heretofore been accomplished by one or more dedicated microprocessors which form the heart of the digital modem. For example, the 9600 baud HST modem manufactured by U.S. Robotics Corporation and described in U.S. Pat. No. 5,008,091 issued on Apr. 16, 1991 employs three microprocessors: (1) a transmitting microprocessor dedicated primarily to the translation of digital data into digital sample values; (2) a receiving microprocessor devoted primarily to the translation of sample amplitude values back into digital data; and (3) a supervisory microprocessor which serves as the interface to the computer to which the modem is connected.